Method and apparatus for cancelling interference and receiving signal in wireless communication system

ABSTRACT

The present invention relates to a wireless communication system. A method for a terminal for receiving a signal by means of NAICS (Network-Assisted Interference Cancellation and Suppression) in a wireless communication system that supports carrier aggregation according to one embodiment of the preset invention comprises the steps of: transmitting terminal capability information comprising band combination information indicating the band combination supported by the terminal on the carrier aggregation; and receiving a signal on the basis of the terminal capability information, wherein the band combination information may comprise directive information indicating whether the UE support the NAICS for the band combination.

TECHNICAL FIELD

The present invention relates to a wireless communication system, andmore particularly, to a method and apparatus for receiving a signal bycancelling interference in a wireless communication system.

BACKGROUND ART

Multiple input multiple output (MIMO) increases the efficiency of datatransmission and reception using multiple transmit antennas and multiplereceive antennas instead of a single transmission antenna and a singlereception antenna. A receiver receives data through multiple paths whenmultiple antennas are used, whereas the receiver receives data through asingle antenna path when a single antenna is used. Accordingly, MIMO canincrease a data transmission rate and throughput and improve coverage.

A single cell MIMO scheme can be classified into a single user-MIMO(SU-MIMO) scheme for receiving a downlink signal by a single UE in onecell and a multi user-MIMO (MU-MIMO) scheme for receiving a downlinksignal by two or more user equipments (UEs).

Channel estimation refers to a procedure for compensating for signaldistortion due to fading to restore a reception signal. Here, the fadingrefers to sudden fluctuation in signal intensity due to multipath-timedelay in a wireless communication system environment. For channelestimation, a reference signal (RS) known to both a transmitter and areceiver is required. In addition, the RS can be referred to as a RS ora pilot signal according to applied standard.

A downlink RS is a pilot signal for coherent demodulation for a physicaldownlink shared channel (PDSCH), a physical control format indicatorchannel (PCFICH), a physical hybrid indicator channel (PHICH), aphysical downlink control channel (PDCCH), etc. A downlink RS includes acommon RS (CRS) shared by all UEs in a cell and a dedicated RS (DRS) fora specific UE. For a system (e.g., a system having extended antennaconfiguration LTE-A standard for supporting 8 transmission antennas)compared with a conventional communication system (e.g., a systemaccording to LTE release-8 or 9) for supporting 4 transmission antennas,DRS based data demodulation has been considered for effectively managingRSs and supporting a developed transmission scheme. That is, forsupporting data transmission through extended antennas, DRS for two ormore layers can be defined. DRS is pre-coded by the same pre-coder as apre-coder for data and thus a receiver can easily estimate channelinformation for data demodulation without separate precodinginformation.

A downlink receiver can acquire pre-coded channel information forextended antenna configuration through DRS but requires a separate RSother than DRS in order to non-pre-coded channel information.Accordingly, a receiver of a system according to LTE-A standard candefine a RS for acquisition of channel state information (CSI), that is,CSI-RS.

DISCLOSURE Technical Problem

An object of the present invention is to provide a method and apparatusfor receiving a signal by cancelling interference in a wirelesscommunication system.

It will be appreciated by persons skilled in the art that the objectsthat could be achieved with the present invention are not limited towhat has been particularly described hereinabove and the above and otherobjects that the present invention could achieve will be more clearlyunderstood from the following detailed description.

Technical Solution

In one aspect of the present invention, a method for receiving a signalusing NAICS (Network-Assisted Interference Cancellation and Suppression)by a user equipment (UE) in a wireless communication system supporting acarrier aggregation may include transmitting UE capability informationincluding band combination information indicating a band combinationsupported by the UE on the carrier aggregation, and receiving the signalbased on the UE capability information. The band combination informationmay include indication information indicating whether the UE support theNAICS for the band combination.

If the indication information is included in the band combinationinformation, it may be indicated that the UE supports NAICS.

The indication information may include a maximum number of componentcarriers (CCs) supporting NAICS in the band combination corresponding tothe band combination information.

The indication information may include a maximum bandwidth supportingNAICS for the band combination corresponding to the band combinationinformation.

The indication information may be configured in a bitmap, and each bitof the bitmap corresponds to a combination of a maximum number ofcomponent carriers (CCs) and a maximum bandwidth.

If the indication information is included in the band combinationinformation, the number of common reference signal (CRS) ports in aninterference cell may be determined to be 2.

In another aspect of the present invention, a UE for receiving a signalusing NAICS in a wireless communication system supporting a carrieraggregation may include a radio frequency (RF) unit, and a processor.The processor may transmit UE capability information including bandcombination information indicating a band combination supported by theUE on the carrier aggregation, and receive the signal based on the UEcapability information. The band combination information may includeindication information indicating whether the UE support the NAICS forthe band combination.

If the indication information is included in the band combinationinformation, it may be indicated that the UE supports NAICS.

The indication information may include a maximum number of componentcarriers (CCs) supporting NAICS in the band combination corresponding tothe band combination information.

The indication information may include a maximum bandwidth supportingNAICS for the band combination corresponding to the band combinationinformation.

The indication information may be configured in a bitmap, and each bitof the bitmap corresponds to a combination of a maximum number ofcomponent carriers (CCs) and a maximum bandwidth.

If the indication information is included in the band combinationinformation, the number of common reference signal (CRS) ports in aninterference cell may be determined to be 2.

Advantageous Effects

According to an embodiment of the present invention, a method andapparatus for receiving a signal by cancelling interference in awireless communication system can be provided.

It will be appreciated by persons skilled in the art that that theeffects that could be achieved with the present invention are notlimited to what has been particularly described hereinabove and otheradvantages of the present invention will be more clearly understood fromthe following detailed description taken in conjunction with theaccompanying drawings.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention.

FIG. 1 illustrates the type-1 radio frame structure;

FIG. 2 illustrates the structure of a downlink resource grid for theduration of one downlink slot;

FIG. 3 illustrates the structure of a downlink subframe;

FIG. 4 illustrates the structure of an uplink subframe;

FIG. 5 illustrates the configuration of a multiple input multiple output(MIMO) communication system having multiple antennas;

FIG. 6 illustrates a conventional common reference signal (CRS) anddedicated reference signal (DRS) pattern;

FIG. 7 illustrates an exemplary demodulation reference signal (DM RS)pattern defined for the long term evolution-advanced (LTE-A) system;

FIG. 8 illustrates exemplary channel state information reference signal(CSI-RS) patterns;

FIG. 9 illustrates an exemplary periodic CSI-RS transmission;

FIG. 10 illustrates an exemplary aperiodic CSI-RS transmission;

FIG. 11 illustrates an example of using two CSI-RS configurations;

FIG. 12 illustrates a general interference environment in a downlinksystem;

FIG. 13 illustrates an exemplary transmission mode (TM) of an adjacentcell according to triggering subframe set information;

FIG. 14 is a flowchart illustrating an embodiment of the presentinvention; and

FIG. 15 is a block diagram of a base station (BS) and a user equipment(UE) to which an embodiment of the present invention is applicable.

BEST MODE

The following embodiments are proposed by combining constituentcomponents and characteristics of the present invention according to apredetermined format. The individual constituent components orcharacteristics should be considered optional factors on the conditionthat there is no additional remark. If required, the individualconstituent components or characteristics may not be combined with othercomponents or characteristics. Also, some constituent components and/orcharacteristics may be combined to implement the embodiments of thepresent invention. The order of operations to be disclosed in theembodiments of the present invention may be changed. Some components orcharacteristics of any embodiment may also be included in otherembodiments, or may be replaced with those of the other embodiments asnecessary.

The embodiments of the present invention are disclosed on the basis of adata communication relationship between a base station and a terminal.In this case, the base station is used as a terminal node of a networkvia which the base station can directly communicate with the terminal.Specific operations to be conducted by the base station in the presentinvention may also be conducted by an upper node of the base station asnecessary.

In other words, it will be obvious to those skilled in the art thatvarious operations for enabling the base station to communicate with theterminal in a network composed of several network nodes including thebase station will be conducted by the base station or other networknodes other than the base station. The term “base station (BS)” may bereplaced with a fixed station, Node-B, eNode-B (eNB), or an access pointas necessary. The term “relay” may be replaced with the terms relay node(RN) or relay station (RS). The term “terminal” may also be replacedwith a user equipment (UE), a mobile station (MS), a mobile subscriberstation (MSS) or a subscriber station (SS) as necessary.

It should be noted that specific terms disclosed in the presentinvention are proposed for convenience of description and betterunderstanding of the present invention, and the use of these specificterms may be changed to other formats within the technical scope orspirit of the present invention.

In some instances, well-known structures and devices are omitted inorder to avoid obscuring the concepts of the present invention andimportant functions of the structures and devices are shown in blockdiagram form. The same reference numbers will be used throughout thedrawings to refer to the same or like parts.

Exemplary embodiments of the present invention are supported by standarddocuments disclosed for at least one of wireless access systemsincluding an institute of electrical and electronics engineers (IEEE)802 system, a 3rd generation partnership project (3GPP) system, a 3GPPlong term evolution (LTE) system, an LTE-advanced (LTE-A) system, and a3GPP2 system. In particular, steps or parts, which are not described toclearly reveal the technical idea of the present invention, in theembodiments of the present invention may be supported by the abovedocuments. All terminology used herein may be supported by at least oneof the above-mentioned documents.

The following embodiments of the present invention can be applied to avariety of wireless access technologies, for example, code divisionmultiple access (CDMA), frequency division multiple access (FDMA), timedivision multiple access (TDMA), orthogonal frequency division multipleaccess (OFDMA), single carrier frequency division multiple access(SC-FDMA), and the like. CDMA may be embodied through wireless (orradio) technology such as universal terrestrial radio access (UTRA) orCDMA2000. TDMA may be embodied through wireless (or radio) technologysuch as global system for mobile communication (GSM)/general packetradio service (GPRS)/enhanced data rates for GSM evolution (EDGE). OFDMAmay be embodied through wireless (or radio) technology such as instituteof electrical and electronics engineers (IEEE) 802.11 (Wi-Fi), IEEE802.16 (WiMAX), IEEE 802-20, and evolved UTRA (E-UTRA). UTRA is a partof universal mobile telecommunications system (UMTS). 3rd generationpartnership project (3GPP) long term evolution (LTE) is a part of E-UMTS(Evolved UMTS), which uses E-UTRA. 3GPP LTE employs OFDMA in downlinkand employs SC-FDMA in uplink. LTE-Advanced (LTE-A) is an evolvedversion of 3GPP LTE. WiMAX can be explained by IEEE 802.16e(wirelessMAN-OFDMA reference system) and advanced IEEE 802.16m(wirelessMAN-OFDMA advanced system). For clarity, the followingdescription focuses on IEEE 802.11 systems. However, technical featuresof the present invention are not limited thereto.

With reference to FIG. 1, the structure of a downlink radio frame willbe described below.

In a cellular orthogonal frequency division multiplexing (OFDM) wirelesspacket communication system, uplink and/or downlink data packets aretransmitted in subframes. One subframe is defined as a predeterminedtime period including a plurality of OFDM symbols. The 3GPP LTE standardsupports a type-1 radio frame structure applicable to frequency divisionduplex (FDD) and a type-2 radio frame structure applicable to timedivision duplex (TDD).

FIG. 1 illustrates the type-1 radio frame structure. A downlink radioframe is divided into 10 subframes. Each subframe is further dividedinto two slots in the time domain. A unit time during which one subframeis transmitted is defined as a Transmission Time Interval (TTI). Forexample, one subframe may be 1 ms in duration and one slot may be 0.5 msin duration. A slot includes a plurality of OFDM symbols in the timedomain and a plurality of resource blocks (RBs) in the frequency domain.Because the 3GPP LTE system adopts OFDMA for downlink, an OFDM symbolrepresents one symbol period. An OFDM symbol may be referred to as anSC-FDMA symbol or symbol period. An RB is a resource allocation unitincluding a plurality of contiguous subcarriers in a slot.

The number of OFDM symbols in one slot may vary depending on a cyclicprefix (CP) configuration. There are two types of CPs: extended CP andnormal CP. In the case of the normal CP, one slot includes 7 OFDMsymbols. In the case of the extended CP, the length of one OFDM symbolis increased and thus the number of OFDM symbols in a slot is smallerthan in the case of the normal CP. Thus when the extended CP is used,for example, 6 OFDM symbols may be included in one slot. If channelstate gets poor, for example, during fast movement of a UE, the extendedCP may be used to further decrease inter-symbol interference (ISI).

In the case of the normal CP, one subframe includes 14 OFDM symbolsbecause one slot includes 7 OFDM symbols. The first two or three OFDMsymbols of each subframe may be allocated to a physical downlink controlchannel (PDCCH) and the other OFDM symbols may be allocated to aphysical downlink shared channel (PDSCH).

The above-described radio frame structures are purely exemplary and thusit is to be noted that the number of subframes in a radio frame, thenumber of slots in a subframe, or the number of symbols in a slot mayvary.

FIG. 2 illustrates the structure of a downlink resource grid for theduration of one downlink slot. FIG. 2 corresponds to a case in which anOFDM includes normal CP. Referring to FIG. 2, a downlink slot includes aplurality of OFDM symbols in the time domain and includes a plurality ofRBs in the frequency domain. Here, one downlink slot includes 7 OFDMsymbols in the time domain and an RB includes 12 subcarriers in thefrequency domain, which does not limit the scope and spirit of thepresent invention. An element on a resource grid is referred to as aresource element (RE). For example, RE a(k,l) refers to RE location in akth subcarrier and a first OFDM symbol. In the case of the normal CP,one RB includes 12×7 REs (in the case of the extended CP, one RBincludes 12×6 REs). An interval between subcarriers is 15 kHz and thusone RB includes about 180 kHz in the frequency domain. NDL is number ofRBs in a downlink slot. NDL depends on a downlink transmission bandwidthconfigured by BS scheduling.

FIG. 3 illustrates the structure of a downlink subframe. Up to threeOFDM symbols at the start of the first slot in a downlink subframe areused for a control region to which control channels are allocated andthe other OFDM symbols of the downlink subframe are used for a dataregion to which a PDSCH is allocated. A basic unit of transmission isone subframe. That is, a PDCCH and a PDSCH are allocated across twoslots. Downlink control channels used in the 3GPP LTE system include,for example, a physical control format indicator channel (PCFICH), aphysical downlink control channel (PDCCH), and a physical hybridautomatic repeat request (HARQ) indicator channel (PHICH). The PCFICH islocated in the first OFDM symbol of a subframe, carrying informationabout the number of OFDM symbols used for transmission of controlchannels in the subframe. The PHICH delivers an HARQACKnowledgment/Negative ACKnowledgment (ACK/NACK) signal in response toan uplink transmission. Control information carried on the PDCCH iscalled downlink control information (DCI). The DCI transports uplink ordownlink scheduling information, or uplink transmission power controlcommands for UE groups. The PDCCH delivers information about resourceallocation and a transport format for a downlink shared channel(DL-SCH), resource allocation information about an uplink shared channel(UL-SCH), paging information of a paging channel (PCH), systeminformation on the DL-SCH, information about resource allocation for ahigher-layer control message such as a random access responsetransmitted on the PDSCH, a set of transmission power control commandsfor individual UEs of a UE group, transmission power controlinformation, voice over Internet protocol (VoIP) activation information,etc. A plurality of PDCCHs may be transmitted in the control region. AUE may monitor a plurality of PDCCHs. A PDCCH is formed by aggregatingone or more consecutive Control Channel Elements (CCEs). A CCE is alogical allocation unit used to provide a PDCCH at a coding rate basedon the state of a radio channel. A CCE corresponds to a plurality of REgroups. The format of a PDCCH and the number of available bits for thePDCCH are determined according to the correlation between the number ofCCEs and a coding rate provided by the CCEs. An eNB determines the PDCCHformat according to DCI transmitted to a UE and adds a cyclic redundancycheck (CRC) to control information. The CRC is masked by an identifier(ID) known as a radio network temporary identifier (RNTI) according tothe owner or usage of the PDCCH. When the PDCCH is directed to aspecific UE, its CRC may be masked by a cell-RNTI (C-RNTI) of the UE.When the PDCCH is for a paging message, the CRC of the PDCCH may bemasked by a paging indicator identifier (P-RNTI). When the PDCCH carriessystem information, particularly, a system information block (SIB), itsCRC may be masked by a system information ID and a system informationRNTI (SI-RNTI). To indicate that the PDCCH carries a random accessresponse in response to a random access preamble transmitted by a UE,its CRC may be masked by a random access-RNTI (RA-RNTI).

FIG. 4 illustrates the structure of an uplink subframe. An uplinksubframe may be divided into a control region and a data region in thefrequency domain. A Physical Uplink Control Channel (PUCCH) carryinguplink control information is allocated to the control region and aphysical uplink shared channel (PUSCH) carrying user data is allocatedto the data region. To maintain the property of a single carrier, a UEdoes not transmit a PUSCH and a PUCCH simultaneously. A PUCCH for a UEis allocated to an RB pair in a subframe. The RBs of the RB pair occupydifferent subcarriers in two slots. Thus it is said that the RB pairallocated to the PUCCH is frequency-hopped over a slot boundary.

Modeling of MIMO System

A multiple input multiple output (MIMO) system increasestransmission/reception efficiency of data using multiple transmission(Tx) antennas and multiple reception (Rx) antennas. MIMO technology doesnot depend upon a single antenna path in order to receive all messagesbut instead can combine a plurality of data fragments received through aplurality of antennas and receive all data.

MIMO technology includes a spatial diversity scheme, a spatialmultiplexing scheme, etc. The spatial diversity scheme can increasetransmission reliability or can widen a cell diameter with diversitygain and thus is appropriate for data transmission of a UE that moves ahigh speed. The spatial multiplexing scheme can simultaneously transmitdifferent data so as to increase data transmission rate without increasein a system bandwidth.

FIG. 5 illustrates the configuration of a MIMO communication systemhaving multiple antennas. As illustrated in FIG. 5(a), the simultaneoususe of a plurality of antennas at both the transmitter and the receiverincreases a theoretical channel transmission capacity, compared to useof a plurality of antennas at only one of the transmitter and thereceiver. Therefore, transmission rate may be increased and frequencyefficiency may be remarkably increased. As channel transmission rate isincreased, transmission rate may be increased, in theory, to the productof a maximum transmission rate R_(o) that may be achieved with a singleantenna and a transmission rate increase Ri.

R _(i)=min(N _(T) ,N _(R))  [Equation 1]

For instance, a MIMO communication system with four Tx antennas and fourRx antennas may achieve a four-fold increase in transmission ratetheoretically, relative to a single-antenna system. Since thetheoretical capacity increase of the MIMO system was verified in themiddle 1990s, many techniques have been actively proposed to increasedata rate in real implementation. Some of the techniques have alreadybeen reflected in various wireless communication standards for 3G mobilecommunications, future-generation wireless local area network (WLAN),etc.

Concerning the research trend of MIMO up to now, active studies areunderway in many respects of MIMO, inclusive of studies of informationtheory related to calculation of multi-antenna communication capacity indiverse channel environments and multiple access environments, studiesof measuring MIMO radio channels and MIMO modeling, studies oftime-space signal processing techniques to increase transmissionreliability and transmission rate, etc.

Communication in a MIMO system will be described in detail throughmathematical modeling. It is assumed that N_(T) Tx antennas and N_(R) Rxantennas are present in the system.

Regarding a transmission signal, up to N_(T) pieces of information canbe transmitted through the N_(T) Tx antennas, as expressed in Equation 2below.

s=└s ₁ ,s ₂ , . . . ,s _(N) _(T) ┘^(T)  [Equation 2]

A different transmission power may be applied to each piece oftransmission information, s₁, s₂, . . . , s_(N) _(T) . Let thetransmission power levels of the transmission information be denoted byP₁, P₂, . . . , P_(N) _(T) , respectively. Then the transmissionpower-controlled transmission information vector is given as

ŝ=[ŝ ₁ ,ŝ ₂ , . . . ,ŝ _(N) _(T) ]^(T) =[P ₁ s ₁ ,P ₂ s ₂ , . . . ,P_(N) _(T) s _(N) _(T) ]^(T)  [Equation 3]

The transmission power-controlled transmission information vector ŝ maybe expressed as follows, using a diagonal matrix P of transmissionpower.

$\begin{matrix}{\hat{s} = {{\begin{bmatrix}P_{1} & \; & \; & 0 \\\; & P_{2} & \; & \; \\\; & \; & \; & \; \\0 & \; & \; & P_{N_{T}}\end{bmatrix}\begin{bmatrix}s_{1} \\s_{2} \\\vdots \\s_{N_{T}}\end{bmatrix}} = {Ps}}} & \lbrack {{Equation}\mspace{14mu} 4} \rbrack\end{matrix}$

N_(T) transmission signals x₁, x₂, . . . , x_(N) _(T) may be generatedby multiplying the transmission power-controlled information vector ŝ bya weight matrix W. The weight matrix W functions to appropriatelydistribute the transmission information to the Tx antennas according totransmission channel states, etc. These N_(T) transmission signals x₁,x₂, . . . , x_(N) _(T) are represented as a vector x, which may bedetermined by Equation 5 below.

$\begin{matrix}{{{x = {\begin{bmatrix}x_{1} \\x_{2} \\\vdots \\x_{i} \\\vdots \\x_{N_{T}}\end{bmatrix} = {{\begin{bmatrix}w_{11} & w_{12} & \ldots & w_{1N_{T}} \\w_{21} & w_{22} & \ldots & w_{2N_{T}} \\\vdots & \; & \ddots & \; \\w_{i\; 1} & w_{i\; 2} & \ldots & w_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\w_{N_{T}1} & w_{N_{T}2} & \ldots & w_{N_{T}N_{T}}\end{bmatrix}\begin{bmatrix}{\hat{s}}_{1} \\{\hat{s}}_{2} \\\vdots \\{\hat{s}}_{j} \\\vdots \\{\hat{s}}_{N_{T}}\end{bmatrix}} =}}}\quad}{\quad{{W\hat{s}} = {WPs}}}} & \lbrack {{Equation}\mspace{14mu} 5} \rbrack\end{matrix}$

Here, w_(ij) refers to a weight between an i_(th) Tx antenna and j_(th)information.

A reception signal x may be considered in different ways according totwo cases (e.g., spatial diversity and spatial multiplexing). In thecase of spatial multiplexing, different signals are multiplexed and themultiplexed signals are transmitted to a receiver, and thus, elements ofinformation vector (s) have different values. In the case of spatialdiversity, the same signal is repeatedly transmitted through a pluralityof channel paths and thus elements of information vectors (s) have thesame value. A hybrid scheme of spatial multiplexing and spatialdiversity can also be considered. That is, that same signal may betransmitted through three Tx antennas and the remaining signals may bespatial-multiplexed and transmitted to a receiver.

In the case of N_(R) Rx antennas, a reception signal of each antenna maybe expressed as the vector shown in Equation 6 below.

y=[y ₁ ,y ₂ , . . . ,y _(N) _(R) ]^(T)  [Equation 6]

When a channel modeling is executed in the MIMO communication system,individual channels can be distinguished from each other according totransmission/reception (Tx/Rx) antenna indexes. A channel passing therange from a Tx antenna j to an Rx antenna i is denoted by h_(ij). Itshould be noted that the index order of the channel h_(ij) is locatedbefore a reception (Rx) antenna index and is located after atransmission (Tx) antenna index.

FIG. 5(b) illustrates channels from N_(T) Tx antennas to an Rx antennai. The channels may be collectively represented in the form of vectorand matrix. Referring to FIG. 5(b), the channels passing the range fromthe N_(T) Tx antennas to the Rx antenna i can be represented by theEquation 7 below.

h _(i) ^(T) =[h _(i1) ,h _(i2) , . . . ,h _(iN) _(T) ]  [Equation 7]

All channels passing the range from the N_(T) Tx antennas to N_(R) Rxantennas are denoted by the matrix shown in Equation 8 below.

$\begin{matrix}{H = {\begin{bmatrix}h_{1}^{T} \\h_{2}^{T} \\\vdots \\h_{i}^{T} \\\vdots \\h_{N_{R}}^{T}\end{bmatrix} = \begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1N_{T}} \\h_{21} & h_{22} & \ldots & h_{2N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 1} & h_{i\; 2} & \ldots & h_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}}} & \lbrack {{Equation}\mspace{14mu} 8} \rbrack\end{matrix}$

Additive white Gaussian noise (AWGN) is added to an actual channel whichhas passed the channel matrix. The AWGN (n₁, n₂, . . . , n_(NR)) addedto each of N_(R) reception (Rx) antennas can be represented by Equation9 below.

n=[n ₁ ,n ₂ , . . . ,n _(N) _(R) ]^(T)  [Equation 9]

A reception signal calculated by the above-mentioned equations can berepresented by Equation 10 below.

$\begin{matrix}{y = {\begin{bmatrix}y_{1} \\y_{2} \\\vdots \\y_{i} \\\vdots \\y_{N_{R}}\end{bmatrix} = {{{\begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1N_{T}} \\h_{21} & h_{22} & \ldots & h_{2N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 1} & h_{i\; 2} & \ldots & h_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}\begin{bmatrix}x_{1} \\x_{2} \\\vdots \\x_{j} \\\vdots \\x_{N_{T}}\end{bmatrix}} + \begin{bmatrix}n_{1} \\n_{2} \\\vdots \\n_{i} \\\vdots \\n_{N_{R}}\end{bmatrix}} = {{Hx} + n}}}} & \lbrack {{Equation}\mspace{14mu} 10} \rbrack\end{matrix}$

The number of rows and the number of columns of a channel matrix Hindicating a channel condition are determined by the number of Tx/Rxantennas. In the channel matrix H, the number of rows is equal to thenumber (N_(R)) of Rx antennas, and the number of columns is equal to thenumber (N_(T)) of Tx antennas. Namely, the channel matrix H is denotedby an N_(R)×N_(T) matrix.

The rank of a matrix is defined as the smaller between the number ofindependent rows and the number of independent columns in the channelmatrix. Accordingly, the rank of the channel matrix is not larger thanthe number of rows or columns of the channel matrix. The rank of achannel matrix H, rank(H) satisfies the following constraint.

rank(H)≦min(N _(T) ,N _(R))  [Equation 11]

For MIMO transmission, ‘rank’ indicates the number of paths forindependent transmission of signals and ‘number of layers’ indicates thenumber of streams transmitted through each path. In general, atransmission end transmits layers, the number of which corresponds tothe number of ranks used for signal transmission, and thus, rank havethe same meaning as number of layers unless there is no differentdisclosure.

Reference Signals (RSs)

In a wireless communication system, a packet is transmitted on a radiochannel. In view of the nature of the radio channel, the packet may bedistorted during the transmission. To receive the signal successfully, areceiver should compensate for the distortion of the reception signalusing channel information. Generally, to enable the receiver to acquirethe channel information, a transmitter transmits a signal known to boththe transmitter and the receiver and the receiver acquires knowledge ofchannel information based on the distortion of the signal received onthe radio channel. This signal is called a pilot signal or an RS.

In the case of data transmission and reception through multipleantennas, knowledge of channel states between transmission (Tx) antennasand reception (Rx) antennas is required for successful signal reception.Accordingly, an RS should be transmitted through each Tx antenna.

RSs in a mobile communication system may be divided into two typesaccording to their purposes: RS for channel information acquisition andRS for data demodulation. Since its purpose lies in that a UE acquiresdownlink channel information, the former should be transmitted in abroad band and received and measured even by a UE that does not receivedownlink data in a specific subframe. This RS is also used in asituation like handover. The latter is an RS that an eNB transmits alongwith downlink data in specific resources. A UE can estimate a channel byreceiving the RS and accordingly can demodulate data. The RS should betransmitted in a data transmission area.

A legacy 3GPP LTE (e.g., 3GPP LTE release-8) system defines two types ofdownlink RSs for unicast services: a common RS (CRS) and a dedicated RS(DRS). The CRS is used for acquisition of information about a channelstate, measurement of handover, etc. and may be referred to as acell-specific RS. The DRS is used for data demodulation and may bereferred to as a UE-specific RS. In a legacy 3GPP LTE system, the DRS isused for data demodulation only and the CRS can be used for bothpurposes of channel information acquisition and data demodulation.

CRSs, which are cell-specific, are transmitted across a wideband inevery subframe. According to the number of Tx antennas at an eNB, theeNB may transmit CRSs for up to four antenna ports. For instance, an eNBwith two Tx antennas transmits CRSs for antenna port 0 and antennaport 1. If the eNB has four Tx antennas, it transmits CRSs forrespective four Tx antenna ports, antenna port 0 to antenna port 3.

FIG. 6 illustrates a CRS and DRS pattern for an RB (including 14 OFDMsymbols in time by 12 subcarriers in frequency in case of a normal CP)in a system where an eNB has four Tx antennas. In FIG. 6, REs labeledwith ‘R0’, ‘R1’, ‘R2’ and ‘R3’ represent the positions of CRSs forantenna port 0 to antenna port 4, respectively. REs labeled with ‘D’represent the positions of DRSs defined in the LTE system.

The LTE-A system, an evolution of the LTE system, can support up toeight Tx antennas. Therefore, it should also support RSs for up to eightTx antennas. Because downlink RSs are defined only for up to four Txantennas in the LTE system, RSs should be additionally defined for fiveto eight Tx antenna ports, when an eNB has five to eight downlink Txantennas in the LTE-A system. Both RSs for channel measurement and RSsfor data demodulation should be considered for up to eight Tx antennaports.

One of significant considerations for design of the LTE-A system isbackward compatibility. Backward compatibility is a feature thatguarantees a legacy LTE terminal to operate normally even in the LTE-Asystem. If RSs for up to eight Tx antenna ports are added to atime-frequency area in which CRSs defined by the LTE standard aretransmitted across a total frequency band in every subframe, RS overheadbecomes huge. Therefore, new RSs should be designed for up to eightantenna ports in such a manner that RS overhead is reduced.

Largely, new two types of RSs are introduced to the LTE-A system. Onetype is CSI-RS serving the purpose of channel measurement for selectionof a transmission rank, a modulation and coding scheme (MCS), aprecoding matrix index (PMI), etc. The other type is demodulation RS (DMRS) for demodulation of data transmitted through up to eight Txantennas.

Compared to the CRS used for both purposes of measurement such aschannel measurement and measurement for handover and data demodulationin the legacy LTE system, the CSI-RS is designed mainly for channelestimation, although it may also be used for measurement for handover.Since CSI-RSs are transmitted only for the purpose of acquisition ofchannel information, they may not be transmitted in every subframe,unlike CRSs in the legacy LTE system. Accordingly, CSI-RSs may beconfigured so as to be transmitted intermittently (e.g. periodically)along the time axis, for reduction of CSI-RS overhead.

When data is transmitted in a downlink subframe, DM RSs are alsotransmitted dedicatedly to a UE for which the data transmission isscheduled. Thus, DM RSs dedicated to a particular UE may be designedsuch that they are transmitted only in a resource area scheduled for theparticular UE, that is, only in a time-frequency area carrying data forthe particular UE.

FIG. 7 illustrates an exemplary DM RS pattern defined for the LTE-Asystem. In FIG. 7, the positions of REs carrying DM RSs in an RBcarrying downlink data (an RB having 14 OFDM symbols in time by 12subcarriers in frequency in case of a normal CP) are marked. DM RSs maybe transmitted for additionally defined four antenna ports, antenna port7 to antenna port 10 in the LTE-A system. DM RSs for different antennaports may be identified by their different frequency resources(subcarriers) and/or different time resources (OFDM symbols). This meansthat the DM RSs may be multiplexed in frequency division multiplexing(FDM) and/or time division multiplexing (TDM). If DM RSs for differentantenna ports are positioned in the same time-frequency resources, theymay be identified by their different orthogonal codes. That is, these DMRSs may be multiplexed in Code Division Multiplexing (CDM). In theillustrated case of FIG. 7, DM RSs for antenna port 7 and antenna port 8may be located on REs of DM RS CDM group 1 through multiplexing based onorthogonal codes. Similarly, DM RSs for antenna port 9 and antenna port10 may be located on REs of DM RS CDM group 2 through multiplexing basedon orthogonal codes.

FIG. 8 illustrates exemplary CSI-RS patterns defined for the LTE-Asystem. In FIG. 8, the positions of REs carrying CSI-RSs in an RBcarrying downlink data (an RB having 14 OFDM symbols in time by 12subcarriers in frequency in case of a normal CP) are marked. One of theCSI-RS patterns illustrated in FIGS. 8(a) to 8(e) is available for anydownlink subframe. CSI-RSs may be transmitted for eight antenna portssupported by the LTE-A system, antenna port 15 to antenna port 22.CSI-RSs for different antenna ports may be identified by their differentfrequency resources (subcarriers) and/or different time resources (OFDMsymbols). This means that the CSI-RSs may be multiplexed in FDM and/orTDM. CSI-RSs positioned in the same time-frequency resources fordifferent antenna ports may be identified by their different orthogonalcodes. That is, these DM RSs may be multiplexed in CDM. In theillustrated case of FIG. 8(a), CSI-RSs for antenna port 15 and antennaport 16 may be located on REs of CSI-RS CDM group 1 through multiplexingbased on orthogonal codes. CSI-RSs for antenna port 17 and antenna port18 may be located on REs of CSI-RS CDM group 2 through multiplexingbased on orthogonal codes. CSI-RSs for antenna port 19 and antenna port20 may be located on REs of CSI-RS CDM group 3 through multiplexingbased on orthogonal codes. CSI-RSs for antenna port 21 and antenna port22 may be located on REs of CSI-RS CDM group 4 through multiplexingbased on orthogonal codes. The same principle described with referenceto FIG. 8(a) is applicable to the CSI-RS patterns illustrated in FIGS.8(b) to 8(e).

The RS patterns illustrated in FIGS. 6, 7 and 8 are purely exemplary.Thus it should be clearly understood that various embodiments of thepresent invention are not limited to specific RS patterns. That is,various embodiments of the present invention can also be implemented inthe same manner when other RS patterns than those illustrated in FIGS.6, 7 and 8 are applied.

CSI-RS Configuration

Among a plurality of CSI-RSs and a plurality of IMRs set to a UE, oneCSI process can be defined in a manner of associating a CSI-RS resourcefor measuring a signal with an interference measurement resource (IMR)for measuring interference. A UE feedbacks CSI information induced fromCSI processes different from each other to a network (e.g., basestation) with an independent period and a subframe offset.

In particular, each CSI process has an independent CSI feedbackconfiguration. The base station can inform the UE of the CS-RS resource,the IMR resource association information and the CSI feedbackconfiguration via higher layer signaling. For example, assume that threeCSI processes shown in Table 1 are set to the UE.

TABLE 1 Signal Measurement CSI Process Resource (SMR) IMR CSI process 0CSI-RS 0 IMR 0 CSI process 1 CSI-RS 1 IMR 1 CSI process 2 CSI-RS 0 IMR 2

In Table 1, a CSI-RS 0 and a CSI-RS 1 indicate a CSI-RS received from acell 1 corresponding to a serving cell of a UE and a CSI-RS receivedfrom a cell 2 corresponding to a neighbor cell participating incooperation, respectively. IMRs set to each of the CSI processes shownin Table 1 are shown in Table 2.

TABLE 2 IMR eNB 1 eNB 2 IMR 0 Muting Data transmission IMR 1 Datatransmission Muting IMR 2 Muting Muting

A cell 1 performs muting in an IMR 0 and a cell 2 performs datatransmission in the IMR 0. A UE is configured to measure interferencefrom other cells except the cell 1 in the IMR 0. Similarly, the cell 2performs muting in an IMR 1 and the cell 1 performs data transmission inthe IMR 1. The UE is configured to measure interference from other cellsexcept the cell 2 in the IMR 1. The cell 1 and the cell 2 perform mutingin an IMR 2 and the UE is configured to measure interference from othercells except the cell 1 and the cell 2 in the IMR 2.

Hence, as shown in Table 1 and Table 2, if data is received from thecell 1, CSI information of the CSI process 0 indicates optimized RI, PMIand CQI information. If data is received from the cell 2, CSIinformation of the CSI process 1 indicates optimized RI, PMI and CQIinformation. If data is received from the cell 1 and there is nointerference from the cell 2, CSI information of the CSI process 2indicates optimized RI, PMI and CQI information.

It is preferable for a plurality of CSI processes set to a UE to sharevalues subordinate to each other. For example, in case of jointtransmission performed by the cell 1 and the cell 2, if a CSI process 1considering a channel of the cell 1 as a signal part and a CSI process 2considering a channel of the cell 2 as a signal part are set to a UE, itis able to easily perform JT scheduling only when ranks of the CSIprocess 1 and the CSI process 2 and a selected subband index areidentical to each other.

A period or a pattern of transmitting a CSI-RS can be configured by abase station. In order to measure the CSI-RS, a UE should be aware ofCSI-RS configuration of each CSI-RS antenna port of a cell to which theUE belongs thereto. The CSI-RS configuration can include a DL subframeindex in which the CSI-RS is transmitted, time-frequency location of aCSI-RS resource element (RE) in a transmission subframe (e.g., theCSI-RS patterns shown in FIGS. 8(a) to 8(e)) and a CSI-RS sequence (asequence used for a CSI-RS usage, the sequence is pseudo-randomlygenerated according to a prescribed rule based on a slot number, a cellID, a CP length and the like), etc. In particular, a plurality of CSI-RSconfigurations can be used by a random (given) base station and the basestation can inform a UE(s) in a cell of a CSI-RS configuration to beused for the UE(s).

Since it is necessary to identify a CSI-RS for each antenna port,resources to which the CSI-RS for each antenna port is transmittedshould be orthogonal to each other. As mentioned earlier with referenceto FIG. 8, the CSI-RS for each antenna port can be multiplexed by theFDM, the TDM and/or the CDM scheme using an orthogonal frequencyresource, an orthogonal time resource and/or an orthogonal coderesource.

When the base station informs the UEs in a cell of information on aCSI-RS (CSI-RS configuration), it is necessary for the base station topreferentially inform the UEs of information on time-frequency to whichthe CSI-RS for each antenna port is mapped. Specifically, information ontime can include numbers of subframes in which a CSI-RS is transmitted,a period of transmitting a CSI-RS, a subframe offset of transmitting aCSI-RS, an OFDM symbol number in which a CSI-RS resource element (RE) ofa specific antenna is transmitted, etc. Information on frequency caninclude a frequency space of transmitting a CSI-RS resource element (RE)of a specific antenna, an RE offset on a frequency axis, a shift value,etc.

FIG. 9 is a diagram for explaining an example of a scheme ofperiodically transmitting a CSI-RS. A CSI-RS can be periodicallytransmitted with a period of an integer multiple of a subframe (e.g.,5-subframe period, 10-subframe period, 20-subframe period, 40-subframeperiod or 80-subframe period).

FIG. 9 shows a radio frame configured by 10 subframes (subframe number 0to 9). In FIG. 9, for example, a transmission period of a CSI-RS of abase station corresponds to 10 ms (i.e., 10 subframes) and a CSI-RStransmission offset corresponds to 3. The offset value may varydepending on a base station to make CSI-RSs of many cells to be evenlydistributed in time domain. If a CSI-RS is transmitted with a period of10 ms, an offset value may have one selected from among 0 to 9.Similarly, if a CSI-RS is transmitted with a period of 5 ms, an offsetvalue may have one selected from among 0 to 4. If a CSI-RS istransmitted with a period of 20 ms, an offset value may have oneselected from among 0 to 19. If a CSI-RS is transmitted with a period of40 ms, an offset value may have one selected from among 0 to 39. If aCSI-RS is transmitted with a period of 80 ms, an offset value may haveone selected from among 0 to 79. The offset value corresponds to a valueof a subframe in which CSI-RS transmission starts by a base stationtransmitting a CSI-RS with a prescribed period. If the base stationinforms a UE of a transmission period of a CSI-RS and an offset value,the UE is able to receive the CSI-RS of the base station at acorresponding subframe position using the transmission period and theoffset value. The UE measures a channel through the received CSI-RS andmay be then able to report such information as a CQI, a PMI and/or an RI(rank indicator) to the base station. In the present invention, the CQI,the PMI and/or the RI can be commonly referred to as CQI (or CSI) excepta case of individually explaining the CQI, the PMI and/or the RI. And,the CSI-RS transmission period and the offset can be separatelydesignated according to a CSI-RS configuration.

FIG. 10 is a diagram for explaining an example of a scheme ofaperiodically transmitting a CSI-RS. In FIG. 10, for example, one radioframe is configured by 10 subframes (subframe number 0 to 9). As shownin FIG. 10, a subframe in which a CSI-RS is transmitted can berepresented as a specific pattern. For example, a CSI-RS transmissionpattern can be configured by a 10-subframe unit and whether to transmita CSI-RS can be indicated by a 1-bit indicator in each subframe. Anexample of FIG. 10 shows a pattern of transmitting a CSI-RS in asubframe index 3 and 4 among 10 subframes (subframe index 0 to 9). Theindicator can be provided to a UE via higher layer signaling.

As mentioned in the foregoing description, configuration of CSI-RStransmission can be variously configured. In order to make a UE properlyreceive a CSI-RS and perform channel measurement, it is necessary for abase station to inform the UE of CSI-RS configuration. Embodiments ofthe present invention for informing a UE of CSI-RS configuration areexplained in the following.

Method of Indicating CSI-RS Configuration

In general, a base station is able to inform a UE of CSI-RSconfiguration by one of two schemes in the following.

A first scheme is a scheme that a base station broadcasts information onCSI-RS configuration to UEs using dynamic broadcast channel (DBCH)signaling.

In a legacy LTE system, when contents on system information are informedto UEs, the information is transmitted to the UEs via a BCH(broadcasting channel). Yet, if the contents are too much and the BCH isunable to carry all of the contents, the base station transmits thesystem information using a scheme used for transmitting a generaldownlink data. And, PDCCH CRC of corresponding data is transmitted in amanner of being masked using SI-RNTI, i.e., system information RNTI,instead of a specific UE ID (e.g., C-RNTI). In this case, actual systeminformation is transmitted to a PDSCH region together with a generalunicast data. By doing so, all UEs in a cell decode PDCCH using theSI-RNTI, decode PDSCH indicated by the corresponding PDCCH and may bethen able to obtain the system information. This sort of broadcastingscheme may be referred to as a DBCH (dynamic BCH) to differentiate itfrom a general broadcasting scheme, i.e., PBCH (physical BCH).

Meanwhile, system information broadcasted in a legacy LTE system can bedivided into two types. One is a master information block (MIB)transmitted on the PBCH and another one is a system information block(SIB) transmitted on a PDSCH region in a manner of being multiplexedwith a general unicast data. In the legacy LTE system, since informationtransmitted with an SIB type 1 to an SIB type 8 (SIB1 to SIB8) arealready defined, it may be able to define a new SIB type to transmitinformation on a CSI-RS configuration corresponding to new systeminformation not defined in the legacy SIB types. For example, it may beable to define SIB9 or SIB10 and the base station can inform UEs withina cell of the information on the CSI-RS configuration via the SIB9 orthe SIB10 using a DBCH scheme.

A second scheme is a scheme that a base station informs each UE ofinformation on CSI-RS configuration using RRC (radio resource control)signaling. In particular, the information on the CSI-RS can be providedto each of the UEs within a cell using dedicated RRC signaling. Forexample, in the course of establishing a connection with the basestation via an initial access or handover of a UE, the base station caninform the UE of the CSI-RS configuration via RRC signaling. Or, whenthe base station transmits an RRC signaling message, which requireschannel status feedback based on CSI-RS measurement, to the UE, the basestation can inform the UE of the CSI-RS configuration via the RRCsignaling message.

Indication of CSI-RS Configuration

A random base station may use a plurality of CSI-RS configurations andthe base station can transmit a CSI-RS according to each of a pluralityof the CSI-RS configurations to a UE in a predetermined subframe. Inthis case, the base station informs the UE of a plurality of the CSI-RSconfigurations and may be able to inform the UE of a CSI-RS to be usedfor measuring a channel state for making a feedback on a CQI (channelquality information) or CSI (channel state information).

Embodiments for a base station to indicate a CSI-RS configuration to beused in a UE and a CSI-RS to be used for measuring a channel areexplained in the following.

FIG. 11 is a diagram for explaining an example of using two CSI-RSconfigurations. In FIG. 11, for example, one radio frame is configuredby 10 subframes (subframe number 0 to 9). In FIG. 11, in case of a firstCSI-RS configuration, i.e., a CSI-RS1, a transmission period of a CSI-RSis 10 ms and a transmission offset of a CSI-RS is 3. In FIG. 11, in caseof a second CSI-RS configuration, i.e., a CSI-RS2, a transmission periodof a CSI-RS is 10 ms and a transmission offset of a CSI-RS is 4. A basestation informs a UE of information on two CSI-RS configurations and maybe able to inform the UE of a CSI-RS configuration to be used for CQI(or CSI) feedback among the two CSI-RS configurations.

If the base station asks the UE to make a CQI feedback on a specificCSI-RS configuration, the UE can perform channel state measurement usinga CSI-RS belonging to the CSI-RS configuration only. Specifically, achannel state is determined based on CSI-RS reception quality, an amountof noise/interference and a function of a correlation coefficient. Inthis case, the CSI-RS reception quality is measured using the CSI-RSbelonging to the CSI-RS configuration only. In order to measure theamount of noise/interference and the correlation coefficient (e.g., aninterference covariance matrix indicating interference direction, etc.),measurement can be performed in a subframe in which the CSI-RS istransmitted or a subframe designated in advance. For example, in theembodiment of FIG. 11, if the base station asks the UE to make afeedback on the first CSI-RS configuration (CSI-RS1), the UE measuresreception quality using a CSI-RS transmitted in a fourth subframe (asubframe index 3) of a radio frame and the UE can be separatelydesignated to use an add number subframe to measure the amount ofnoise/interference and the correlation coefficient. Or, it is able todesignate the UE to measure the CSI-RS reception quality, the amount ofnoise/interference and the correlation coefficient in a specific singlesubframe (e.g., a subframe index 3) only.

For example, reception signal quality measured using a CSI-RS can besimply represented by SINR (signal-to-interference plus noise ratio) asS/(I+N) (in this case, S corresponds to strength of a reception signal,I corresponds to an amount of interference and N corresponds to anamount of noise). The S can be measured through a CSI-RS in a subframeincluding the CSI-RS in a subframe including a signal transmitted to aUE. Since the I and the N change according to an amount of interferencereceived from a neighbor cell, direction of a signal received from aneighbor cell, and the like, the I and the N can be measured by an SRStransmitted in a subframe in which the S is measured or a separatelydesignated subframe, etc.

In this case, the amount of noise/interference and the correlationcoefficient can be measured in a resource element (RE) in which a CRSbelonging to a corresponding subframe or a CSI-RS is transmitted. Or, inorder to easily measure noise/interference, the noise/interference canbe measured through a configured null RE. In order to measurenoise/interference in a CRS or CSI-RS RE, a UE preferentially recovers aCRS or a CSI-RS and subtracts a result of the recovery from a receptionsignal to make a noise and interference signal to be remained only. Bydoing so, the UE is able to obtain statistics of noise/interference fromthe remained noise and the interference signal. A null RE may correspondto an empty RE (i.e., transmission power is 0 (zero)) in which no signalis transmitted by a base station. The null RE makes other base stationsexcept the corresponding base station easily measure a signal. In orderto measure an amount of noise/interference, it may use all of a CRS RE,a CSI-RS RE and a null RE. Or, a base station may designate REs to beused for measuring noise/interference for a UE. This is because it isnecessary to properly designate an RE to be used for measuringnoise/interference measured by the UE according to whether a signal of aneighbor cell transmitted to the RE corresponds to a data signal or acontrol signal. Since the signal of the neighbor cell transmitted to theRE varies according to whether or not synchronization between cells ismatched, a CRS configuration, a CSI-RS configuration and the like, thebase station identifies the signal of the neighbor cell and may be ableto designate an RE in which measurement is to be performed for the UE.In particular, the base station can designate the UE to measurenoise/interference using all or a part of the CRS RE, the CSI-RS RE andthe null RE.

For example, the base station may use a plurality of CSI-RSconfigurations and may be able to inform the UE of a CSI-RSconfiguration to be used for CQI feedback and a null RE position whileinforming the UE of one or more CSI-RS configurations. In order todistinguish the CSI-RS configuration to be used for CQI feedback by theUE from a null RE transmitted by zero transmission power, the CSI-RSconfiguration to be used for CQI feedback by the UE may correspond to aCSI-RS configuration transmitted by non-zero transmission power. Forexample, if the base station informs the UE of a CSI-RS configuration inwhich the UE performs channel measurement, the UE can assume that aCSI-RS is transmitted by non-zero transmission power in the CSI-RSconfiguration. In addition, if the base station informs the UE of aCSI-RS configuration transmitted by zero transmission power (i.e., nullRE position), the UE can assume that an RE position of the CSI-RSconfiguration corresponds to zero transmission power. In other word,when the base station informs the UE of a CSI-RS configuration ofnon-zero transmission power, if there exists a CSI-RS configuration ofzero transmission power, the base station can inform the UE of acorresponding null RE position.

As a modified example of the method of indicating a CSI-RSconfiguration, the base station informs the UE of a plurality of CSI-RSconfigurations and may be able to inform the UE of all or a part ofCSI-RS configurations to be used for CQI feedback among a plurality ofthe CSI-RS configurations. Hence, having received a request for CQIfeedback on a plurality of the CSI-RS configurations, the UE measures aCQI using a CSI-RS corresponding to each CSI-RS configuration and may bethen able to transmit a plurality of CQI information to the basestation.

Or, in order to make the UE transmit a CQI for each of a plurality ofthe CSI-RS configurations, the base station can designate an uplinkresource, which is necessary for the UE to transmit the CQI, in advanceaccording to each CSI-RS configuration. Information on the uplinkresource designation can be provided to the UE in advance via RRCsignaling.

Or, the base station can dynamically trigger the UE to transmit a CQIfor each of a plurality of CSI-RS configurations to the base station.Dynamic triggering of CQI transmission can be performed via PDCCH. Itmay inform the UE of a CSI-RS configuration for which a CQI is to bemeasured via PDCCH. Having received the PDCCH, the UE can feedback a CQImeasurement result measured for the CSI-RS configuration designated bythe PDCCH to the base station.

A transmission timing of a CSI-RS corresponding to each of a pluralityof the CSI-RS configurations can be designated to be transmitted in adifferent subframe or an identical subframe. If CSI-RSs according toCSI-RS configurations different from each other are designated to betransmitted in an identical subframe, it may be necessary to distinguishthe CSI-RSs from each other. In order to distinguish the CSI-RSsaccording to the CSI-RS configurations different from each other, it maybe able to differently apply at least one selected from the groupconsisting of a time resource, a frequency resource and a code resourceof CSI-RS transmission. For example, an RE position in which a CSI-RS istransmitted can be differently designated in a subframe according to aCSI-RS configuration (e.g., a CSI-RS according to one CSI-RSconfiguration is designated to be transmitted in an RE position shown inFIG. 8 (a) and a CSI-RS according to another CSI-RS configuration isdesignated to be transmitted in an RE position shown in FIG. 8 (b))(distinction using a time and frequency resource). Or, if CSI-RSsaccording to CSI-RS configurations different from each other aretransmitted in an identical RE position, the CSI-RSs can bedistinguished from each other by differently using a CSI-RS scramblingcode in the CSI-RS configurations different from each other (distinctionusing a code resource).

UE Capability Information Element

An LTE system, for example, an LTE-release 10 system may use mainlycarrier aggregation (CA) and higher-layer MIMO in order to increaseperformance. A UE supporting this system may support CA and MIMO spatialdivision multiple access (MIMO SDMA). Such UEs may be classified intoUEs having a high level capability and UEs having a low level capabilitydepending on how much they support CA and MIMO SDMA. To transmitinformation about a capability that a UE has to a BS, a UE capabilityinformation element including various fields such as UE category may beused.

For example, the UE capability information element may include asupported MIMO-capability field. The supported MIMO-capability fieldincludes information about the number of layers supported for spatialmultiplexing on DL. A different MIMO capability may be configured perbandwidth, per band, or per band combination by the use of the supportedMIMO-capability field.

The UE capability information element may further include the UEcategory field. The UE category field may define a UL capability and aDL capability for each of UEs under category 1 to category 8.Specifically, the UE category field may include a UL physical parametervalue and a DL physical parameter value for a UE of each category. Eventhough UEs of categories 6, 7, and 8 do not support CA, they may includean rf-parameters field in the UE capability information element.

Carrier Aggregation (CA)

CA refers to assignment of a plurality of carriers to a UE. A componentcarrier (CC) is a carrier used in a CA system and may be referred toshortly as a carrier. For example, two 20-MHz CCs may be allocated toassign a 40-MHz bandwidth.

CA may be classified into inter-band CA and intra-band CA.

In inter-band CA, CCs of different bands are aggregated, whereas inintra-band CA, CCs of the same frequency band are aggregated.

Intra-band CA is further branched into intra-band contiguous CA andintra-band non-contiguous CA depending on whether aggregated CCs arecontiguous.

Meanwhile, the following operating bands are defined for UL and DL inthe 3GPP LTE/LTE-A system.

TABLE 3 E- Downlink (DL) UTRA Uplink (UL) operating band operating bandOper- BS receive BS transmit Dup- ating UE transmit UE receive lex BandF_(UL) _(—) _(low)-F_(UL) _(—) _(high) F_(DL) _(—) _(low)-F_(DL) _(—)_(high) Mode  1 1920 MHz-1980 MHz 2110 MHz-2170 MHz FDD  2 1850 MHz-1910MHz 1930 MHz-1990 MHz FDD  3 1710 MHz-1785 MHz 1805 MHz-1880 MHz FDD  41710 MHz-1755 MHz 2110 MHz-2155 MHz FDD  5 824 MHz-849 MHz 869 MHz-894MHz FDD   6¹ 830 MHz-840 MHz 875 MHz-885 MHz FDD  7 2500 MHz-2570 MHz2620 MHz-2690 MHz FDD  8 880 MHz-915 MHz 925 MHz-960 MHz FDD  9 1749.9MHz-1784.9 MHz 1844.9 MHz-1879.9 MHz FDD 10 1710 MHz-1770 MHz 2110MHz-2170 MHz FDD 11 1427.9 MHz-1447.9 MHz 1475.9 MHz-1495.9 MHz FDD 12699 MHz-716 MHz 729 MHz-746 MHz FDD 13 777 MHz-787 MHz 746 MHz-756 MHzFDD 14 788 MHz-798 MHz 758 MHz-768 MHz FDD 15 Reserved Reserved FDD 16Reserved Reserved FDD 17 704 MHz-716 MHz 734 MHz-746 MHz FDD 18 815MHz-830 MHz 860 MHz-875 MHz FDD 19 830 MHz-845 MHz 875 MHz-890 MHz FDD20 832 MHz-862 MHz 791 MHz-821 MHz FDD 21 1447.9 MHz-1462.9 MHz 1495.9MHz-1510.9 MHz FDD 22 3410 MHz-3490 MHz 3510 MHz-3590 MHz FDD 23 2000MHz-2020 MHz 2180 MHz-2200 MHz FDD 24 1626.5 MHz-1660.5 MHz 1525MHz-1559 MHz FDD 25 1850 MHz-1915 MHz 1930 MHz-1995 MHz FDD 26 814MHz-849 MHz 859 MHz-894 MHz FDD 27 807 MHz-824 MHz 852 MHz-869 MHz FDD28 703 MHz-748 MHz 758 MHz-803 MHz FDD 29 N/A 717 MHz-728 MHz FDD² . . .33 1900 MHz-1920 MHz 1900 MHz-1920 MHz TDD 34 2010 MHz-2025 MHz 2010MHz-2025 MHz TDD 35 1850 MHz-1910 MHz 1850 MHz-1910 MHz TDD 36 1930MHz-1990 MHz 1930 MHz-1990 MHz TDD 37 1910 MHz-1930 MHz 1910 MHz-1930MHz TDD 38 2570 MHz-2620 MHz 2570 MHz-2620 MHz TDD 39 1880 MHz-1920 MHz1880 MHz-1920 MHz TDD 40 2300 MHz-2400 MHz 2300 MHz-2400 MHz TDD 41 2496MHz 2690 MHz 2496 MHz 2690 MHz TDD 42 3400 MHz-3600 MHz 3400 MHz-3600MHz TDD 43 3600 MHz-3800 MHz 3600 MHz-3800 MHz TDD 44 703 MHz-803 MHz703 MHz-803 MHz TDD

In [Table 3], F_(UL) _(_) _(low) represents the lowest frequency of a ULoperating band, and F_(UL) _(_) _(high) represents the highest frequencyof the UL operating band. F_(DL) _(_) _(low) represents the lowestfrequency of a DL operating band, and F_(DL) _(_) _(high) represents thehighest frequency of the DL operating band.

If operating bands are set as listed in [Table 3], the frequencydistribution organization of each country may assign a specificfrequency to a service provider according to its situation.

Meanwhile, CA bandwidth classes and their corresponding guard bands aregiven as follows.

TABLE 4 Aggregated CA Transmission Maximum Bandwidth Bandwidth number ofNominal Guard Class Configuration CC Band BW_(GB) A N_(RB,agg) ≦100 10.05 BW_(Channel(1)) B N_(RB,agg) ≦100 2 FFS C 100 < N_(RB,agg) ≦ 200 20.05 max (BW_(Channel(1)), BW_(Channel(2))) D 200 < N_(RB,agg) ≦ [300]FFS FFS E [300] < N_(RB,agg) ≦ [400] FFS FFS F [400] < N_(RB,agg) ≦[500] FFS FFS

In [Table 4], [ ] represents that a numeral value is variable, FFS isshort for For Further Study, and N_(RB) _(_) _(agg) represents thenumber of RBs aggregated in an aggregated channel band.

The following table lists an example of CA Configurations and theircorresponding bandwidth sets, in the case of intra-band contiguous CA.

TABLE 5 E-UTRA CA configuration/Bandwidth combination set Maximumaggregated Bandwidth E-UTRA CA 50RB + 100RB 75RB + 75RB 75RB + 100RB100RB + 100RB bandwidth Combination Configuration (10 MHz + 20 MHz) (15MHz + 15 MHz) (15 MHz + 20 MHz) (20 MHz + 20 MHz) [MHz] Set CA_1C YesYes 40 0 CA_7C Yes Yes 40 0 CA_38C Yes Yes 40 0 CA_40C Yes Yes Yes 40 0CA_41C Yes Yes Yes Yes 40 0

In [Table 5], CA Configuration represents an operating band and a CAbandwidth class. For example, CA_1C indicates Operating Band 1 in [Table3] and CA Bandwidth Class C in [Table 4].

[Table 6] below lists an example of CA Configurations and theircorresponding bandwidth sets, in the case of inter-band CA.

TABLE 6 E-UTRA CA configuration/Bandwidth combination set Maximum E-aggregated Bandwidth E-UTRA CA UTRA bandwidth combination ConfigurationBands 1.4 MHz 3 MHz 5 MHz 10 MHz 15 MHz 20 MHz [MHz] set CA_1A-5A 1 Yes20 0 5 Yes CA_1A-18A 1 Yes Yes Yes Yes 35 0 18 Yes Yes Yes CA_1A-19A 1Yes Yes Yes Yes 35 0 19 Yes Yes Yes CA_1A-21A 1 Yes Yes Yes Yes 35 0 21Yes Yes Yes CA_2A-17A 2 Yes Yes 20 0 17 Yes Yes CA_2A-29A 2 Yes Yes 29Yes Yes Yes CA_3A-5A 3 Yes Yes Yes 30 0 5 Yes Yes 3 Yes 20 1 5 Yes YesCA_3A-7A 3 Yes Yes Yes Yes 40 0 7 Yes Yes Yes CA_3A-8A 3 Yes Yes Yes 300 8 Yes Yes 3 Yes 20 1 8 Yes Yes CA_3A-20A 3 Yes Yes Yes Yes 30 0 20 YesYes CA_4A-5A 4 Yes Yes 20 0 5 Yes Yes CA_4A-7A 4 Yes Yes 30 0 7 Yes YesYes Yes CA_4A-12A 4 Yes Yes Yes Yes 20 0 12 Yes Yes CA_4A-13A 4 Yes YesYes Yes 30 0 13 Yes 4 Yes Yes 20 1 13 Yes CA_4A-17A 4 Yes Yes 20 0 17Yes Yes CA_4A-29A 4 Yes Yes 29 Yes Yes Yes CA_5-12 5 Yes Yes 12 Yes YesCA_5A-17A 5 Yes Yes 20 0 17 Yes Yes CA_7A-20A 7 Yes Yes Yes 30 0 20 YesYes CA_8A-20A 8 Yes Yes 20 Yes Yes CA_11A-18A 11 Yes Yes 18 Yes Yes Yes

In [Table 6], for example, the first CA Configuration, CA_1A-5Aindicates that CCs of Operating Band 1 in [Table 3] and CA BandwidthClass A in [Table 4] are aggregated with CCs of Operating Band 5 in[Table 3] and CA Bandwidth Class A in [Table 4].

Interference Cancellation Method

FIG. 12 illustrates a general interference environment in a DL system.

For the convenience of description, a cell managed by TP A is referredto as cell A, and a user communicating with TP A is referred to as UE a.Likewise, cell B and UE b exist for an adjacent TP, TP B. Because cell Aand cell B use the same radio resources, UE b located at a cell edge isinterfered by cell A. Hereinafter, cell A is referred to as aninterference cell, TP A is referred to as an interference TP, cell B isreferred to as a serving cell, TP B is referred to as a serving TP, andUE b is referred to as a NAICS (Network-Assisted InterferenceCancellation and Suppression) UE.

A NAICS UE is defined as a UE capable of increasing a data receptionrate by cancelling an interference signal received from an interferencecell.

In order to effectively cancel interference, the NAICS UE should haveknowledge of various interference parameters (IPs) regarding theinterference signal. For example, information about a control formatindicator (CFI), a multimedia broadcast multicast service singlefrequency network (MBSFN) configuration, an RI, a CRS AP, a cell ID, amodulation order, an MCS, an RNTI, a transmission mode (TM), and so onis required in a NAICS environment independent of TMs. In a CRS TM NAICSenvironment, information about a PMI, a data to RS EPRE, a PA, a PB, asystem bandwidth, a PDSCH allocation, and so on is required. Also in aDM-RS TM NAICS environment, information about a PDSCH bandwidth forDM-RS, a data to RS EPRE, a PB, DMRS APs, nSCID, CSI-RS presence andtheir pattern, a virtual cell ID, and so on is required. Meanwhile, theserving cell may receive the IPs needed to perform NAICS from theadjacent cell through a backhaul or the like.

The NAICS UE cancels an interference signal by receiving the IPs throughthe serving TP or the interference TP or detecting the IPs by blinddetection (BD). However, if all necessary IPs are received, signalingoverhead and complexity may be increased significantly. Moreover, if BDis performed for some IPs, inaccurate values may be detected, therebyfailing to cancel an interference signal successfully.

As a solution to the above problem, the values of some IPs may berestricted in advance through network coordination. That is, the UE mayperform BD for a value of an IP only within a restricted set.

Embodiment 1

An embodiment of the present invention relates to a method for reportinga UE capability regarding an interference TM, and a method forimplicitly indicating interference TM information to a UE using a UEcapability by a BS.

It is ideal that a NAICS UE is capable of performing NAICS with respectto all interference TMs. Considering an actual UE complexity, however,many UEs have a NAICS capability only for a specific interference TM ora specific interference TM set. For example, a specific UE may performNAICS by detecting IPs only for CRS-based interference TMs, TMs 2, 3, 4,5, and 6 through BD, without the capability of performing NAICS for theother interference TMs. In other words, the interference TMs that the UEsupports are TMs 2, 3, 4, 5, and 6. Other UEs may be able to performNAICS only for DMRS-based interference TMs, TMs 8, 9, and 10.

One of methods for enabling a UE to efficiently perform NAICS is that aTM set used by an interference cell is restricted and indicated to theUE. For example, if the interference cell uses only TMs 2 and 3,information about the TMs 2 and 3 is indicated to the UE, and the UE maydetermine whether to perform NAICS by comparing its NAICS capabilitywith the interference TMs. However, this method requires additionalsignaling to indicate an interference TM.

In Embodiment 1, methods for implicitly indicating to a UE whether a TMof an interference cell is included in TMs supported by the UE, withoutadditional signaling regarding information about the TM of theinterference cell will be described.

Embodiment 1-1

Embodiment 1-1 of the present invention relates to a method fortransmitting information about supported TMs by a UE and transmittingnetwork assistance information only to a UE that will perform NAICSbased on the information by a BS. Thus, the UE may implicitly determinewhether a TM of an interference cell is included in the supported TMs ofthe UE. A detailed description will be given below of Embodiment 1-1.

If different UEs support different interference TMs, it is preferablefor the UEs to report their NAICS capability information includinginformation about supported interference TMs of the UEs to the BS.

The BS determines whether a specific UE will perform NAICS based onreceived information about supported interference TMs of the UE, andtransmits network assistance information only to a UE that will performNAICS.

That is, upon receipt of the network assistance information, a UE may beimplicitly aware that a TM of an interference cell is included insupported TMs of the UE.

For example, it is assumed that UE1 and UE2 experiencing severeinterference from interference cell A exist in a serving cell, andreport TMs 2, 3, 4, 5, and 6, and TMs 8, 9, and 10, respectively astheir supported interference TMs. If only LTE release-8 UEs exist ininterference cell A and thus interference cell A uses only CRS-based TMs(TM 2, 3, 4, 5, and 6), UE2 does not perform NAICS successfully.Therefore, the serving cell transmits network assistance informationabout interference cell A only to UE1 so that only UE1 may performNAICS. In other words, the serving cell does not transmit the networkassistance information to UE2, thereby not allowing UE2 to performNAICS.

In other words, if a UE has not received the network assistanceinformation, the UE does not perform NAICS, assuming that a TM of theinterference BS is not included in supported interference TMs of the UE.On the other hand, if the UE has received the network assistanceinformation, the UE performs NAICS, assuming that the TM of theinterfering BS is included in the supported interference TMs of the UE.

In Embodiment 1-1, the LTE release-8 UEs may move out of interferencecell A and LTE release-11 UEs may enter interference cell A, withpassage of time. In this case, as the TM of the interference cell ischanged, UE2 may receive network assistance information and thus performNAICS. On the other hand, having received the network assistanceinformation at the time when cell A includes only the release-8 UEs, UE1may not perform NAICS any longer. Therefore, it is preferable toindicate to UE1 that the previous network assistance informationreceived by UE1 is not valid any longer, by RRC signaling. Upon receiptof this information, UE1 may not perform NAICS. Or a valid duration maybe set for the transmitted (e.g., RRC-signaled) network assistanceinformation. If the network assistance information is not updated withinthe valid duration, the UE may determine that the previously receivednetwork assistance information is not valid.

In another method regarding a TM of an interference cell, a UE mayperform NAICS on the assumption that its TM is always identical to aninterference TM. To support this method, a BS may configure a specificfrequency resource area to which the same TM is to be applied throughcooperation between BSs through a backhaul, and perform UE schedulingaccording to the configured value. In this case, although the BS haslimitations in resource allocation, signaling overhead is advantageouslyreduced.

Also, when the UE receives TM information about the interference cell,the BD performance of IPs may be changed according to an interference TMset. For example, high-accuracy BD may be possible for TM set A, whereasthe accuracy of BD may be decreased for TM set B. Accordingly, it may berestricted that resource allocation (RA) granularities of interferencePDSCHs are different for TM set A and TM set B. For example, BDperformance may be increased by allowing PRB-wise scheduling for Set Awithout any special restriction on the RA of the interference cell, andrestricting scheduling on an RBG basis, PRG basis, or subband basis forSet B.

While the UE reports supported interference TM information on a setbasis in the above description, this is purely exemplary. If the UEsupports only one interference TM, the UE may report only one value. Forexample, if the UE is able to eliminate only a TM-4 interference PDSCH,the UE reports only TM 4 as a supported interference TM.

In addition, the UE may report its supported interference TM and itsdesired PDSCH TM at the moment in a pair. For example, only when itsdesired PDSCH TM satisfies a specific condition, the UE may performNAICS for TM-9 interference. The specific condition may be, for example,DMRS-based TMs (TMs 8, 9, and 10).

Additionally, the UE may report, as a capability, whether it is capableof performing NAICS only when its TM is identical to an interference TMto be cancelled or even when the two TMs are different (in the case of amixed TM).

The NAICS UE capability information may include information about thenumber of NAICS-possible CRS ports of an interference cell as well as asupported interference TM. For example, a UE computation capability maybe considered. Thus, a UE having a low computation capability may reportthat it is capable of performing NAICS only for one and two CRS ports ofan interference cell, and a UE having a high computation capability mayreport that it is capable of performing NAICS for one, two, and four CRSports of an interference cell.

Also in a specific example, the UE may transmit a variable n indicatingthe number of NAICS-possible CRS ports of an interference cell in UEcapability information. In another example, the UE may transmit aspecific field (supportedNAICS-2CRS-AP) indicating that a NAICSoperation is possible for two CRS antenna ports in UE capabilityinformation. If the specific field is included in the UE capabilityinformation, it may be determined that the number of CRS ports in theinterference cell is 2.

Embodiment 1-2

Embodiment 1-2 relates to a method for implicitly signaling informationabout a TM of an adjacent cell by transmitting MBSFN subframeinformation about the adjacent cell to a NAICS UE (by higher-layersignaling). For example, the UE may assume that the interference celltransmits a signal in a subframe indicated as an MBSFN subframe in aDM-RS-based TM and in a subframe not indicated as an MBSFN subframe in aCRS-based TM. Hereinbelow, Embodiment 1-2 will be described in detail.

LTE Release-12 considers a technique for supporting different TM setsfor different subframe sets due to the TM detection capabilities ofNAICS UEs. In the LTE system, TMs are classified largely into CRS-basedTMs and DM-RS-based TMs. Accordingly, a method for distinguishing thetwo types of TMs from each other on a subframe set basis may be used.

It is preferable not to transmit CRSs in a PDSCH region in a subframeset for which a DM-RS-based TM is allowed because a CRS-based TM doesnot exist in the subframe set. This may be supported by MBSFNsubframe-based unicast transmission introduced to LTE Release-9.

Therefore, TMs of an adjacent cell may be classified into CRS-based TMsand DM-RS-based TMs, and different subframe sets may be matched to thetwo types of TMs. In this manner, information about subframe sets mayprovide interference TM information implicitly.

For example, if a NAICS UE receives MBSFN subframe information about anadjacent cell which is a target for NAICS, the NAICS UE assumes that aDM-RS-based TM is applied to an MBSFN subframe of the adjacent cell anda CRS-based TM is applied to a non-MBSFN subframe of the adjacent cell.

Embodiment 1-3

Embodiment 1-3 of the present invention relates to a method forimplicitly signaling interference TM information to a UE, using atriggering subframe set by a BS.

If a TM is restricted on a subframe set basis for an adjacent cell, tooa strict constraint may be imposed on scheduling of the adjacent cell.

Therefore, a serving cell indicates triggering subframe set informationindicating that a CRS-based TM or a DM-RS-based TM starts in an adjacentcell to a NAICS UE (by higher-layer signaling). For example, the BSindicates the period and offset of a triggering subframe to the NAICSUE. The NAICS UE may determine a TM of the adjacent cell used until thenext period by detecting DM-RSs in a triggering subframe.

FIG. 13 illustrates an exemplary TM of an adjacent cell according totriggering subframe set information.

Referring to FIG. 13, the adjacent cell manages a triggering subframeset with a predetermined periodicity of T. if a DM-RS is detected attime k, this means that a DM-RS-based TM is applied during a time periodof T corresponding to time k. Subsequently, if a DM-RS is not detectedat time k+1 in the next period, a CRS-based TM is assumed for acorresponding time period of T.

That is, the NAICS UE searches for a DM-RS using a VCID of the adjacentcell at each time instant of a specific subframe set. Upon detection ofa DM-RS, the NAICS UE assumes a DM-RS-based TM for a time period of T,and otherwise, the NAICS UE assumes a CRS-based TM for the time periodof T.

To enable the NAICS UE to easily determine a TM by DM-RS detection, theadjacent cell preferably performs DM-RS-based scheduling or DM-RS+dummysignal transmission in a corresponding subframe.

According to Embodiment 1-3, the scheduling constraint imposed on theadjacent cell may be relieved to within a time unit of T.

Further, if Embodiment 1-3 of the present invention is applied, thetriggering subframe set may be configured as an MBSFN subframe set. Asdescribed in Embodiment 1-2 of the present invention, no CRS is detectedin a subframe set for which a DM-RS-based TM is allowed and this may besupported by MBSFN subframe-based unicast. That is, the NAICS UEdetermines a TM by attempting DM-RS detection at each time instant ofthe triggering subframe set, and does not perform additional detectionof a CRS-based TM and a NAICS operation. This is because TM decision inthe triggering subframe set leads to determination of a subsequent timeperiod of T and thus detection accuracy should be high. Therefore,interference is relieved by restricting signal transmission in aCRS-based TM in the triggering subframe set, thereby increasing DM-RSdetection accuracy.

Further, when Embodiment 1-3 of the present invention is applied, theadjacent cell may be configured to transmit a dummy CSI-RS for which aninitial value of a sequence, VCID is variable, and a different TM setmay be meant for each VCID.

In Embodiment 1-3 of the present invention, if a TM is determined byDM-RS detection in the first subframe of each time period of T,detection accuracy may be decreased due to interference between DM-RSsof a plurality of antenna ports of the adjacent cell. Thus, the adjacentcell may be configured to transmit a dummy CSI-RS for which an initialvalue of a sequence, VCID is variable, and a different TM set may bemeant for each VCID.

However, UEs serviced by the adjacent cell cannot use dummy CSI-RSsbecause the VCID is changed, and the adjacent cell should set ZP CSI-RSsat positions of a CSI-RS pattern corresponding to the dummy CSI-RSs.

The NAICS UE detects dummy CSI-RSs in a triggering subframe set anddetermines information about TMs supported during the next time periodof T according to the VCID of the detected CSI-RSs. In addition, themapping relationship between a VCID and a TM set may be set to bedifferent for each frequency resource unit and indicated to the NAICSUE. The NAICS UE may detect the VCID of a dummy CSI-RS on a frequencyresource unit, thereby determining TM information about thecorresponding frequency resources.

Embodiment 2

Embodiment 2 of the present invention proposes a method for reporting aNAICS capability to a BS in specific consideration of a CA capability bya UE having both the CA capability and the NAICS capability.

For example, the UE may report whether it can support NAICS or report amaximum number of NAICS-supportable CCs, per band per band combination.In the case of band combination of CA_1A-5A in the example of [Table 6],the UE may report whether NAICS is supported for each CC of the includedbands 1A and 5A and the maximum number of supported CCs.

Or more elaborately, the UE may report a NAICS capability independentlyper bandwidth per band per band combination.

For example, the UE may report whether NAICS is supported or the maximumnumber of CCs for which NAICS is supported, per bandwidth per band perband combination.

In addition, it is obvious that the technical feature of reporting aNAICS capability per band per band combination or per bandwidth per bandper band combination is applicable to a higher level, that is, per bandcombination.

According to Embodiment 2 of the present invention, a UE may report aNAICS capability independently for each CC which may be aggregated. As aconsequence, the UE may be implemented more flexibly. For example, a UEhaving low processing power may report that it is capable of performingNAICS only for one of two CCs that can be aggregated, and a UE havinghigh processing power may report that it is capable of performing NAICSfor the two CCs.

First, an exemplary specific method for reporting a NAICS capability perband per band combination is illustrated in [Table 7], [Table 8] and[Table 9].

Referring to [Table 7], a NAICSsupported-r12 is added toBandParameters-v12 defined in BandCombinationParameters-v12, so that theUE may report a NAICS capability for a corresponding band by turningon/off a NAICS function. That is, the NAICSsupported-r12 field for eachband may indicate whether the UE supports NAICS in the band.

TABLE 7 UE-EUTRA-Capability-v12-IEs ::= SEQUENCE {pdcp-Parameters-v12 PDCP-Parameters-v12,phyLayerParameters-v12 PhyLayerParameters-v12 OPTIONAL,rf-Parameters-v12 RF-Parameters-v12,measParameters-v12 MeasParameters-v12,interRAT-ParametersCDMA2000-v12 IRAT-ParametersCDMA2000-v12,otherParameters-r12 Other-Parameters-r12,fdd-Add-UE-EUTRA-Capabilities-v12    UE-EUTRA-CapabilityAddXDD-Mode-v12OPTIONAL,tdd-Add-UE-EUTRA-Capabilities-v12    UE-EUTRA-CapabilityAddXDD-Mode-v12OPTIONAL, nonCriticalExtension SEQUENCE { } OPTIONAL } RF-Parameters-v12::= SEQUENCE {supportedBandCombination-v12 SupportedBandCombination-v12 OPTIONAL }SupportedBandCombination-v12 ::= SEQUENCE (SIZE (1..maxBandComb-r10)) OFBandCombinationParameters-v12 BandCombinationParameters-v12 ::= SEQUENCE{ multipleTimingAdvance-r12 ENUMERATED {supported}  OPTIONAL,simultaneousRx-Tx-r12 ENUMERATED {supported}  OPTIONAL,bandParameterList-r12 SEQUENCE (SIZE (1..maxSimultaneousBands-r10)) OFBandParameters-v12 OPTIONAL, ... } BandParameters-v12 ::= SEQUENCE {supportedCSI-Proc-r12 ENUMERATED {n1, n3, n4} NAICSsupported-r12 BOOLEAN}

In another method, if the NAICS function is on, the UE may report aspecific NAICS capability additionally. For example, BandParameters maybe defined as illustrated in [Table 8] below.

TABLE 8 BandParameters-v12 ::= SEQUENCE {supportedCSI-Proc-r12  ENUMERATED {n1, n3, n4}supportedNAICS-Capability-r12 NAICS-Capability-r12 OPTIONAL }

In [Table 8], NAICS-capability-r12 is a field indicating the NAICScapability of the UE, which may specify a NAICS receiver type, asupported interference TM, the number of supported interference CRSports, and so on.

The NAICS receiver type may indicate a type such as SLIC, R-ML, ML, orEnhanced MMSE IRC receiver. The supported interference TM refers to TMinformation about an interference signal for which the UE is capable ofperforming NAICS, as described before. The number of supportedinterference CRS ports, n means that the UE is capable of performingNAICS for an interference cell transmitting n-port CRSs. That is, if n=1or 2, the UE is capable of performing NAICS for an interference celltransmitting 1- or 2-port CRSs, and if n=1, 2, or 4, the UE is capableof performing NAICS for an interference cell transmitting 1-, 2-, or4-port CRSs.

If NAICS-capability-r12 is not reported for a band, this implies thatthe NAICS function is off for the band.

Also, the UE may report the maximum number of NAICS-supported CCs in aspecific band, per band per band combination. For example, RRC signalingmay be defined as described in [Table 9]. That is, theNAICSsupported-r12 field for each band indicates the maximum number ofCCS that the UE supports in the band.

TABLE 9 BandParameters-v12 ::= SEQUENCE {supportedCSI-Proc-r12 ENUMERATED {n1, n3, n4} NAICSsupported-r12 ENUMERATED {n0, n1, n2, n3, ...} }

If the signaling as described in [Table 9] is used, a NAICS capabilitymay be reported more elaborately for a CC of contiguous intra-band CA.For example, if contiguous intra-band CA is performed in band 1 usingBandwidth Class C, it is possible to support NAICS only for one of twoCCs of band 1. That is, if the UE sets NAICSsupported-r12 for band 1C to1, the UE indicates to the BS that it supports NAICS only for one of thetwo CCs of band 1.

Further from the method, the UE should be able to report a NAICScapability independently for each CC of intra-band non-contiguous CA.For example, the UE should be able to report a NAICS capabilityindependently for intra-band CA with (2A, 2A), as illustrated in FIG.14.

For this purpose, as the UE reports a MIMO capability independently perbandwidth per band per band combination, the UE should be able to reporta NAICS capability independently per bandwidth per band per bandcombination.

That is, the UE preferably reports a NAICS capability independently forthe left CC and the right CC in FIG. 14.

Therefore, [Table 7], [Table 8], and [Table 9] describing NAICScapability reporting per band per band combination may be extendedrespectively to [Table 10], [Table 11], and [Table 12] describing NAICScapability reporting per bandwidth per band per band combination.

[Table 10] below corresponds to [Table 7], describing reporting whethera NAICS capability is supported per bandwidth per band per bandcombination.

TABLE 10 BandParametersDL-v12::=SEQUENCE (SIZE(1..maxBandwidthClass-r12)) OF CA-NAICS-ParametersDL-r12CA-NAICS-ParametersDL-r12 ::= SEQUENCE {   ca-BandwidthClassDL-r12 CA-BandwidthClass-r12,   NAICSsupported-r12    BOOLEAN }

[Table 11] below corresponds to [Table 8], describing further reportingof a specific NAICS capability per bandwidth per band per bandcombination in the case where the NAICS function is on.

TABLE 11 BandParametersDL-v12::=SEQUENCE (SIZE(1..maxBandwidthClass-r12)) OF CA-NAICS-ParametersDL-r12CA-NAICS-ParametersDL-r12 ::= SEQUENCE {ca-BandwidthClassDL-r12 CA-BandwidthClass-r12,supportedNAICS-Capability-r12  NAICS-Capability-r12    OPTIONAL }

[Table 12] below corresponds to [Table 9], describing reporting themaximum number of CCs supporting the NAICS function, per bandwidth perband per band combination.

TABLE 12 BandParametersDL-v12::=SEQUENCE (SIZE(1..maxBandwidthClass-r12)) OF CA-NAICS-ParametersDL-r12CA-NAICS-ParametersDL-r12 ::= SEQUENCE {   ca-BandwidthClassDL-r12  CA-BandwidthClass-r12,   NAICSsupported-r12   ENUMERATED {n0, n1, n2, n3, ...} }

As described before, the feature of reporting a NAICS capability perband per band combination in [Table 7], [Table 8], and [Table 9] is alsoapplicable to reporting a NAICS capability at a higher level, that is,per band combination. For example, a parameter for reporting a NAICScapability may be included in a BandCombination parameter in [Table 7],[Table 8], and [Table 9].

Meanwhile, different MIMO capabilities may be defined depending onwhether NAICS is performed or not.

If the UE performs NAICS, the UE uses a part of total spatial resourcesachievable with the number of its reception antennas in receiving aninterference signal. As a result, only a part of the total spatialresources are used in receiving desired data. That is, a MIMO capabilitydepends on the maximum number of layers in which desired data isspatially multiplexed.

On the contrary, if the UE does not perform NAICS, all of the totalspatial resources may be used for reception of the desired data, therebyincreasing the MIMO capability.

For example, a NAICS UE with four reception antennas may report two MIMOcapabilities corresponding to NAICS and non-NAICS. That is, the UE mayreport maximum 2 layer spatial division multiplexing (SDM) as a MIMOcapability in the case where the NAICS function is on, and maximum 4layer SDM as a MIMO capability in the case where the NAICS function isoff.

Further, the NAICS UE may just report the number of CCs for which NAICSis possible in a different manner from in the examples of [Table 7],[Table 8], and [Table 9] in which whether NAICS is possible or thenumber of NAICS-possible CCs is reported per band per band combination.

That is, if the number of NAICS-possible CCs is N, the BS transmits anecessary network assistance signal for each of the N CCs to the UE. Ifthe number of NAICS-possible CCs is 0, this implies that the UE cannotperform NAICS for any CC.

For example, signaling may be defined as described in [Table 13]. In[Table 13], NAICSsupported-r12 indicates the maximum number of CCs thatthe NAICS UE is capable of supporting.

TABLE 13 UE-EUTRA-Capability-v12-IEs ::= SEQUENCE {pdcp-Parameters-v12 PDCP-Parameters-v12,phyLayerParameters-v12 PhyLayerParameters-v12 OPTIONAL,rf-Parameters-v12 RF-Parameters-v12,measParameters-v12 MeasParameters-v12, interRAT-ParametersCDMA2000-v12IRAT-ParametersCDMA2000-v12, otherParameters-r12 Other-Parameters-r12,fdd-Add-UE-EUTRA-Capabilities-v12   UE-EUTRA-CapabilityAddXDD-Mode-v12OPTIONAL,tdd-Add-UE-EUTRA-Capabilities-v12   UE-EUTRA-CapabilityAddXDD-Mode-v12OPTIONAL, nonCriticalExtension SEQUENCE { }  OPTIONAL }RF-Parameters-v12 ::= SEQUENCE { NAICSsupported-r12 ENUMERATED {n0, n1,n2, n3, ...} }

In the scheme illustrated in [Table 13], if the UE reports n0, the UEdoes not perform NAICS irrespective of whether it actually performs CA.

Further, if a CA-enabled UE receives a DL service in one CC withoutactual CA implementation, the UE may perform NAICS using the resultingextra processing power.

Specifically, for example, if a CA-enabled UE performs CA for four orfewer CCs out of five CCs, the UE has more extra processing powerbecause the number of used CCs is decreased. The UE may perform NAICSfor more CCs using the extra processing power. For example, if four CCsare aggregated, the UE may perform NAICS for one CC. If two CCs areaggregated, the UE may perform NAICS for the two CCs. In this context,it is preferred to report the maximum number of NAICS-possible CCs foreach number of actual aggregated CCs, for effective NAICS capabilityreporting.

In another method, the UE may independently report the maximum number ofNAICS-possible CCs in the case of CA and whether NAICS is possible inthe case of non-CA.

Additionally, the UE may report the maximum number of layers to whichNAICS will be applied per band per band combination to the BS. Thenumber of layers is the sum of the number of layers of a desired PDSCHand the number of layers of an interference PDSCH. For example, in thecase where the maximum number of layers is 3, if the number of desiredPDSCH layers is 1, up to two interference PDSCH layers may be canceled,and if the number of desired PDSCH layers is 2, up to one interferencePDSCH layer may be cancelled.

For example, RRC signaling as described in [Table 14] may be used. In[Table 14], NAICSsupported-r12 indicates the maximum number of layers ina corresponding band, to which the NAICS UE will apply NAICS.

TABLE 14 BandParameters-v12 ::= SEQUENCE { supportedCSI-Proc-r12  ENUMERATED {n1, n3, n4} NAICSsupported-r12    ENUMERATED {n1, n2, n3, ...} }

Likewise, the UE may report the maximum number of layers to which NAICSwill be applied, per bandwidth per band per band combination, to the BSby extending the contents of [Table 14].

For example, RRC signaling as described in [Table 15] may be used.

TABLE 15 BandParametersDL-v12::=SEQUENCE (SIZE(1..maxBandwidthClass-r12)) OF CA-NAICS-ParametersDL-r12CA-NAICS-ParametersDL-r12 ::= SEQUENCE {ca-BandwidthClassDL-r12  CA-BandwidthClass-r12, NAICSsupported-r12  ENUMERATED {n1, n2, n3, ...} }

In the above example, the number of layers to which NAICS is to beapplied is the sum of the number of desired PDSCH layers and the numberof interference PDSCH layers to be cancelled. In another method, thenumber of layers may be defined as the maximum number of interferencePDSCH layers to be cancelled. In this case, 0 may be included as anavailable value of ENUMERATED of NAICSsupported-r12 in [Table 14] and[Table 15].

Further, although only the number of layers to which NAICS is to beapplied is expressed in [Table 14] and [Table 15], the number ofNAICS-supportable CCs as well as the number of layers may be included bycombining [Table 14] and [Table 15] with [Table 9] and [Table 12]. It isalso obvious that the signaling may be combined with the signaling ofanother example, for reporting.

Although the number of layers is reported per band per band combinationor per bandwidth per band per band combination, it may be reported moreaccurately per CC.

In another reporting method, the UE may indicate whether it isNAICS-capable or not by a 1-bit indicator. If CA is applied, the UE andthe BS may interpret the 1-bit indicator as follows.

If the NAICS capability indicator is 1, the UE may apply NAICS to atleast one CC. The BS is not aware of the number of CCs for which the UEwill actually perform NAICS and signals NAICS information about every CCin case NAICS is performed for all CCs. The UE finally determines thenumber of CCs for which NAICS will be performed, and performs NAICSusing NAICS information about a corresponding CC. If the NAICScapability indicator is 0, the UE may not apply NAICS to any CC.

Or the NAICS capability indicator may be interpreted as follows.

If the NAICS capability indicator is 1, the UE may apply NAICS to atleast one CC. The BS is not aware of the number of CCs for which the UEwill actually perform NAICS, selects a part of CCs to which NAICS willbe applied, and signals NAICS information in the corresponding CCs. TheUE finally determines the number of CCs for which NAICS will beperformed, and performs NAICS using NAICS information about acorresponding CC. If the NAICS capability indicator is 0, the UE may notapply NAICS to any CC.

The 1-bit indicator is NAICSsupported-r12 which may be defined asdescribed in [Table 16].

TABLE 16 UE-EUTRA-Capability-v12-IEs ::= SEQUENCE {  pdcp-Parameters-v12 PDCP-Parameters-v12, phyLayerParameters-v12 PhyLayerParameters-v12 OPTIONAL, rf-Parameters-v12 RF-Parameters-v12, naics-Capability-v12 NAICS-Capability-v12 measParameters-v12 MeasParameters-v12,  interRAT-ParametersCDMA2000-v12IRAT-ParametersCDMA2000-v12,  otherParameters-r12 Other-Parameters-r12, fdd-Add-UE-EUTRA-Capabilities-v12   UE-EUTRA-CapabilityAddXDD-Mode-v12OPTIONAL, tdd-Add-UE-EUTRA-Capabilities-v12   UE-EUTRA-CapabilityAddXDD-Mode-v12OPTIONAL,  nonCriticalExtension SEQUENCE{ }   OPTIONAL }NAICS-Capability-v12::=  SEQUENCE { NAICSsupported-r12 BOOLEAN }

In another reporting method, the UE may indicate whether it isNAICS-capable per band combination by a 1-bit indicator. If CA isapplied, the UE and the BS may interpret the 1-bit indicator as follows.

If the NAICS capability indicator is 1, the UE may apply NAICS to atleast one CC of a corresponding band combination. The BS is not aware ofthe number of CCs for which the UE will actually perform NAICS andsignals NAICS information about every CC of a corresponding bandcombination in case NAICS is performed for all CCs of the bandcombination. The UE finally determines the number of CCs for which NAICSwill be performed in the band combination, and performs NAICS usingNAICS information about a corresponding CC. If the NAICS capabilityindicator is 0, the UE may not apply NAICS to any CC of the bandcombination.

Or the 1-bit indicator may be interpreted as follows.

If the NAICS capability indicator is 1, the UE may apply NAICS to atleast one CC of a corresponding band combination. The BS is not aware ofthe number of CCs for which the UE will actually perform NAICS, selectsa part of CCs to which NAICS will be applied from among all CCs of theband combination, and signals NAICS information. The UE finallydetermines the number of CCs for which NAICS will be performed in theband combination, and performs NAICS using NAICS information about acorresponding CC. If the NAICS capability indicator is 0, the UE may notapply NAICS to any CC of the band combination.

The 1-bit indicator is NAICSsupported-r12 which may be defined asdescribed in [Table 17].

TABLE 17 UE-EUTRA-Capability-v12-IEs ::= SEQUENCE { pdcp-Parameters-v12 PDCP-Parameters-v12, phyLayerParameters-v12 PhyLayerParameters-v12  OPTIONAL, rf-Parameters-v12 RF-Parameters-v12, measParameters-v12 MeasParameters-v12, interRAT-ParametersCDMA2000-v12 IRAT-ParametersCDMA2000-v12,otherParameters-r12  Other-Parameters-r12, fdd-Add-UE-EUTRA-Capabilities-v12  UE-EUTRA-CapabilityAddXDD-Mode-v12OPTIONAL, tdd-Add-UE-EUTRA-Capabilities-v12  UE-EUTRA-CapabilityAddXDD-Mode-v12OPTIONAL,  nonCriticalExtension  SEQUENCE { }  OPTIONAL }SupportedBandCombination-v12::=SEQUENCE(SIZE(1..maxBandComb-r10)) OFBandCombinationParameters-v12 BandCombinationParameters-v12 ::= SEQUENCE{  NAICSsupported-r12  BOOLEAN  multipleTimingAdvance-r12 ENUMERATED{supported}  OPTIONAL,  simultaneousRx-Tx-r12  ENUMERATED{supported}  OPTIONAL,  bandParameterList-r12   SEQUENCE (SIZE(1..maxSimultaneousBands-r10)) OF BandParameters-v12 OPTIONAL,  ... }

In another method, the UE indicates whether NAICS is possible by a 1-bitindicator. If CA is applied, both the UE and the BS interpret that NAICSis not possible irrespective of the 1-bit indicator.

In another reporting method, the UE reports a bandwidth (BW) for whichNAICS is possible as well as whether NAICS is possible. That is, the UEmay report NAICS-supportable aggregated BW.

For example, if the UE reports that it is NAICS-capable for 20 MHz, theBS configures CCs so that the sum of BWs may become 20 MHz or less, andtransmits NAICS information corresponding to the CCs to the UE. Or aNAICS-possible BW may be reported per PRB.

A NAICS-possible total BW may be reported per band combination, per bandper band combination, or per bandwidth per band per band combination.

The NAICS-possible total BW may be reported together with the maximumnumber of NAICS-possible CCs. For example, a UE capability may bereported in a supportedNAICS field configured as an 8-bit bitmap, andeach bit of the supportedNAICS field may indicate a predeterminedcombination of a NAICS-possible total BW and the maximum number ofNAICS-possible CCs. In a specific example, the first bit ofsupportedNAICS may indicate 50 PRBs and 5 respectively as aNAICS-possible total BW and the maximum number of NAICS-possible CCs. Ifthe first bit is 1, it may indicate that there is a corresponding NAICScapability.

FIG. 14 is a flowchart illustrating an embodiment of the presentinvention.

Referring to FIG. 14, a UE first transmits UE capability informationindicating a NAICS capability supported by the UE (S141). The UEcapability information transmitted by the UE may include a plurality ofparameters which have been described in Embodiment 1 or Embodiment 2 ofthe present invention. The parameters included in the UE capabilityinformation have been described in detail in Embodiment 1 or Embodiment2 and thus will not be described in detail herein.

Subsequently, the UE receives a signal from a BS based on the UEcapability information (S413). Also, the UE may receive a signal usingreceived network assistance information corresponding to the transmittedUE capability information.

FIG. 15 is a diagram for a BS and a UE capable of being applied to anembodiment of the present invention.

If a relay is included in a wireless communication system, communicationis performed between a base station and the relay in backhaul link andcommunication is performed between the relay and a user equipment inaccess link. Hence, the base station and the user equipment shown in thedrawing can be replaced with the relay in accordance with a situation.

Referring to FIG. 15, a wireless communication system includes a basestation (BS) 1510 and a user equipment (UE) 1520. The BS 1510 includes aprocessor 1513, a memory 1514 and a radio frequency (RF) unit 1511/1512.The processor 1513 can be configured to implement the proposedfunctions, processes and/or methods. The memory 1514 is connected withthe processor 1513 and then stores various kinds of informationassociated with an operation of the processor 1513. The RF unit 1516 isconnected with the processor 1513 and transmits and/or receives a radiosignal. The user equipment 1520 includes a processor 1523, a memory 1524and a radio frequency (RF) unit 1521/1522. The processor 1523 can beconfigured to implement the proposed functions, processes and/ormethods. The memory 1524 is connected with the processor 1523 and thenstores various kinds of information associated with an operation of theprocessor 1523. The RF unit 1521/1522 is connected with the processor1523 and transmits and/or receives a radio signal. The base station 1510and/or the user equipment 1520 may have a single antenna or multipleantennas.

The above-described embodiments correspond to combinations of elementsand features of the present invention in prescribed forms. And, therespective elements or features may be considered as selective unlessthey are explicitly mentioned. Each of the elements or features can beimplemented in a form failing to be combined with other elements orfeatures. Moreover, it is able to implement an embodiment of the presentinvention by combining elements and/or features together in part. Asequence of operations explained for each embodiment of the presentinvention can be modified. Some configurations or features of oneembodiment can be included in another embodiment or can be substitutedfor corresponding configurations or features of another embodiment. And,it is apparently understandable that an embodiment is configured bycombining claims failing to have relation of explicit citation in theappended claims together or can be included as new claims by amendmentafter filing an application.

In this disclosure, a specific operation explained as performed by aneNode B may be performed by an upper node of the eNode B in some cases.In particular, in a network constructed with a plurality of networknodes including an eNode B, it is apparent that various operationsperformed for communication with a user equipment can be performed by aneNode B or other networks except the eNode B. ‘eNode B (eNB)’ may besubstituted with such a terminology as a fixed station, a Node B, a basestation (BS), an access point (AP) and the like.

Embodiments of the present invention can be implemented using variousmeans. For instance, embodiments of the present invention can beimplemented using hardware, firmware, software and/or any combinationsthereof. In the implementation by hardware, a method according to eachembodiment of the present invention can be implemented by at least oneselected from the group consisting of ASICs (application specificintegrated circuits), DSPs (digital signal processors), DSPDs (digitalsignal processing devices), PLDs (programmable logic devices), FPGAs(field programmable gate arrays), processor, controller,microcontroller, microprocessor and the like.

In case of the implementation by firmware or software, a methodaccording to each embodiment of the present invention can be implementedby modules, procedures, and/or functions for performing theabove-explained functions or operations. Software code is stored in amemory unit and is then drivable by a processor.

The memory unit is provided within or outside the processor to exchangedata with the processor through the various means known in public.

Detailed explanation on the preferred embodiment of the presentinvention disclosed as mentioned in the foregoing description isprovided for those in the art to implement and execute the presentinvention. While the present invention has been described andillustrated herein with reference to the preferred embodiments thereof,it will be apparent to those skilled in the art that variousmodifications and variations can be made therein without departing fromthe spirit and scope of the invention. For instance, those skilled inthe art can use each component described in the aforementionedembodiments in a manner of combining it with each other. Hence, thepresent invention may be non-limited to the aforementioned embodimentsof the present invention and intends to provide a scope matched withprinciples and new characteristics disclosed in the present invention.

While the present invention has been described and illustrated hereinwith reference to the preferred embodiments thereof, it will be apparentto those skilled in the art that various modifications and variationscan be made therein without departing from the spirit and scope of theinvention. Thus, it is intended that the present invention covers themodifications and variations of this invention that come within thescope of the appended claims and their equivalents. And, it isapparently understandable that an embodiment is configured by combiningclaims failing to have relation of explicit citation in the appendedclaims together or can be included as new claims by amendment afterfiling an application.

INDUSTRIAL APPLICABILITY

The present invention can be used for a wireless communication devicesuch as a terminal, a relay, a base station and the like.

1. A method for receiving a signal using NAICS (Network-AssistedInterference Cancellation and Suppression) by a user equipment (UE) in awireless communication system supporting a carrier aggregation, themethod comprising; transmitting UE capability information including bandcombination information indicating a band combination supported by theUE on the carrier aggregation; and receiving the signal based on the UEcapability information, wherein the band combination informationincludes indication information indicating whether the UE support theNAICS for the band combination.
 2. The method according to claim 1,wherein if the indication information is included in the bandcombination information, it is indicated that the UE supports NAICS. 3.The method according to claim 1, wherein the indication informationincludes a maximum number of component carriers (CCs) supporting NAICSin the band combination corresponding to the band combinationinformation.
 4. The method according to claim 1, wherein the indicationinformation includes a maximum bandwidth supporting NAICS for the bandcombination corresponding to the band combination information.
 5. Themethod according to claim 1, wherein the indication information isconfigured in a bitmap, and each bit of the bitmap corresponds to acombination of a maximum number of component carriers (CCs) and amaximum bandwidth.
 6. The method according to claim 1, wherein if theindication information is included in the band combination information,the number of common reference signal (CRS) ports in an interferencecell is determined to be
 2. 7. A user equipment (UE) for receiving asignal using NAICS (Network-Assisted Interference Cancellation andSuppression) in a wireless communication system supporting a carrieraggregation, the UE comprising; a radio frequency (RF) unit; and aprocessor, wherein the processor transmits UE capability informationincluding band combination information indicating a band combinationsupported by the UE on the carrier aggregation, and receives the signalbased on the UE capability information, and wherein the band combinationinformation includes indication information indicating whether the UEsupport the NAICS for the band combination.
 8. The UE according to claim7, wherein if the indication information is included in the bandcombination information, it is indicated that the UE supports NAICS. 9.The UE according to claim 7, wherein the indication information includesa maximum number of component carriers (CCs) supporting NAICS in theband combination corresponding to the band combination information. 10.The UE according to claim 7, wherein the indication information includesa maximum bandwidth supporting NAICS for the band combinationcorresponding to the band combination information.
 11. The UE accordingto claim 7, wherein the indication information is configured in abitmap, and each bit of the bitmap corresponds to a combination of amaximum number of component carriers (CCs) and a maximum bandwidth. 12.The UE according to claim 7, wherein if the indication information isincluded in the band combination information, the number of commonreference signal (CRS) ports in an interference cell is determined to be2.